The purpose of the proposed work is to determine if and how surgical technique, specifically initial soft tissue balance and passive kinematics, relates to patient functional and clinical outcomes following total knee arthroplasty (TKA), a common surgical procedure used to treat degenerative joint diseases such as osteoarthritis. An estimated 300,000 TKAs were performed in the United States in 2003, and approximately 3.48 million annual procedures are expected by the year 2030. The success of TKA depends on many factors including the alignment of the prosthetic components and the management (or balancing) of soft tissues around the knee. While TKA is generally successful at restoring function and improving quality of life, a wide gap still separates those who cannot perform basic activities of daily living like comfortably climbing the stairs within their homes to those who can go back to activities they love such as hiking, golfing, or playing tennis. Patients following TKA have functional challenges that are not seen in aged-matched controls, such as climbing stairs more slowly, stiff-knee gait, quadriceps weakness, and abnormal knee kinematics. The source of the abnormal kinematics and the variability in clinical outcomes following total knee arthroplasty remains unknown. Even though surgical technique is believed to be important to the outcome of a TKA, key intra-operative decisions are subjectively and qualitatively performed, representing a significant gap in the current knowledge of the procedure. This lack of objective and quantitative key intra-operative measurements make it difficult to consistently apply the same technique to different patients. Studies of in-vivo function and clinical outcomes of patients following TKA have typically lacked the measurements of patient-specific surgical technique or the pre-operative condition of the joint. While surgeons obviously have a keen sense of what is good and unacceptable surgical technique, it remains unknown how subtle differences in their actions during surgery influence post-operative outcome. This grant will determine if and how objective and quantitative intra-operative measurements of passive kinematics and initial soft tissue balance are associated with post-operative outcomes. Aim 1 will intra- operatively characterize joint stability before and after total knee arthroplasty with a navigation system and novel measurement equipment with a repeatable, objective, experimental procedure. Aim 2 will relate intra- operative measurements of joint stability and passive knee kinematics to patient's joint moments walking and climbing stairs during 6-month and 2-year follow-up examinations in a gait laboratory, using a patient's pre- operative gait as a covariate in the analysis. Aim 3 will relate intra-operative measurements of joint stability and passive knee kinematics to 6-month and 2-year clinical outcomes, as determined by SF-36 and KOOS self- administered assessments by 3 functional measures: a timed Stair Climbing Test, a 6 Minute Walk Test, and a Timed Up and Go test. For these clinical assessments, a patient's pre-operative scores on the same clinical tests will be used as a covariate in the analysis. This study represents an important first step toward improving post-operative outcomes through a comprehensive and rigorous study of intra-operative conditions of the joint and their influence on post- operative joint biomechanics and functional clinical outcomes. These results will enable surgeons to make more informed, evidence-based, intra-operative decisions; physical therapists to individualize rehabilitation programs; and patients will gain realistic expectations of their own specific outcomes.